Narrative:

On preflight O2 check; noticed pressure dropped rapidly; then recovered about 20 psi. I had been taught that this was an indication of the O2 valve not fully open. We asked for a mechanic; explaining that we had a question about the valve. When the mechanic came into the cockpit; he told us that he had checked the valve on the way up; and found it almost closed. I don't know how many flights the aircraft had flown since the O2 system had been worked on; but asking other pilots; few seem to know to check for the recovery of pressure as a sign of insufficient flow through the valve. I believe the fleet needs communication on this potentially disastrous mistake; and maintenance needs training emphasized.

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Original NASA ASRS Text

Title: First Officer reported that some crew oxygen shut off valves are not restored properly after servicing and how to diagnose such a situation.

Narrative: On preflight O2 check; noticed pressure dropped rapidly; then recovered about 20 PSI. I had been taught that this was an indication of the O2 valve not fully open. We asked for a mechanic; explaining that we had a question about the valve. When the mechanic came into the cockpit; he told us that he had checked the valve on the way up; and found it almost closed. I don't know how many flights the aircraft had flown since the O2 system had been worked on; but asking other pilots; few seem to know to check for the recovery of pressure as a sign of insufficient flow through the valve. I believe the fleet needs communication on this potentially disastrous mistake; and maintenance needs training emphasized.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.